Journeyman Electrician Practice Exam

When the outer sheath of Type MI cable is made of steel, what must be provided?

1. A grounding conductor within the cable

2. A separate equipment grounding conductor

3. No additional grounding is necessary

4. A fault current detection system

The correct answer is: A separate equipment grounding conductor

When Type MI (Mineral Insulated) cable has an outer sheath made of steel, it is essential to provide a separate equipment grounding conductor. This requirement arises because the steel sheath can become energized if there is a fault, and a separate grounding conductor helps ensure that any fault current has a safe pathway to ground. The presence of an equipment grounding conductor is crucial for safety, as it helps to prevent electric shock hazards, potential fire risks, and ensures proper functioning of protection devices like circuit breakers. This grounding conductor is distinct from any conductors that may exist within the cable itself, offering an additional layer of safety in the electrical installation. Understanding the need for grounding in MI cable systems highlights the importance of proper grounding practices in the overall safety and reliability of electrical installations. It also showcases why simply relying on the sheath as a grounding mechanism may not be adequate in scenarios with potential fault conditions.